Method of forming center sections for hollow propeller blades



June 26, 1956 F. A. GRUETJEN METHOD OF FORMING CENTER SECTIONS FOR HOLLOW PROPELLER BLADES 4 Sheets-Sheet 1 Filed May 15, 1950 IN V EN TOR.

FrederickAGrueffen flnm /fiwv ATTORNEYi June 26, 1956 F. A. GRUETJEN METHOD OF FORMING CENTER SECTIONS FOR HOLLOW PROPELLER BLADES 4 Sheets-Sheet 2 Filed May 15,

ay/Kg INVENT FrederickACir n ATTORNEYS.

June 26, 1956 F. A. GRUETJEN 2,751,667

METHOD OF FORMING CENTER SECTIONS FOR HOLLOW PROPELLER BLADES Filed May 15, 1950 4 Sheets-Sheet 3 IN V EN TOR. F'edez'ick A.Grue f en BY WW Aw ATTORNEYS June 26, 1956 F. A. GRUETJEN METHOD OF FORMING CENTER SECTIONS FOR HOLLOW PROPELLER BLADES 4 Sheets-Sheet 4 Filed May 15, 1950 mm t Q ATTORNEYS United States METHOD OF FORMING (IENTER SECTIONS FOR HOLLOW PROPELLER BLADES Application May 15, 1950, Serial No. 161,987

1 Claim. (Cl. 29-1563) This invention relates to a method of forming articles such as center foil sections for hollow propeller blades for aircraft.

It is generally recognized that large size hollow propeller blades for aircraft require internal strengthening means of one form or another in order to make the same suit able for the rigid service required. One form of such means heretofore employed has comprised a network of transverse and longitudinal ribs which are welded to the inner surfaces of the blade sections wherever strength and rigidity may be necessary. A structure of this type, while serving the purpose desired, is costly to fabricate in that the bracing members are generally formed separately from the blade proper and must then be secured, as by welding, to the inner surface of the blade.

An object of this invention is to provide a propeller blade center section wherein the longitudinal strengthening ribs are formed integral with and from the same blanks from which the section is formed.

A further object is to provide hollow propeller blades in which the center sections, including integral longitudinal strengthening ribs, are formed in halves which are subsequently fiash welded together to form the completed sections.

Another object is to provide a method of forming strengthening ribs or beads on generally light weight structural elements which is relatively economical to practice and which provides substantially rigid unitary structural elements requiring a minimum number of operations to fabricate.

These and other objects of the invention will appear hereinafter in connection with the following description of embodiments of the invention illustrated in the accompanying drawings in which:

Figure l is a perspective view showing the blank from which a half center section is formed;

Fig. 2 is a top plan view of a blank after the first forging operation;

Fig. 3 is a side elevation of the blank shown in Fig. 2, illustrating the taper of the beads;

Fig. 4 is a transverse sectional view taken along line 4-4 of Fig. 2;

Fig. 5 is a corresponding section taken along line 5-5 of Fig. 2;

Fig. 6 is a top plan view of the blank after the first rolling step;

Fig. 7 is a side elevation of the blank illustrated in Fig. 6, showing the decreased taper of the beads and the taper of the body of the blank;

Fig. 8 is a transverse section taken along line 8-8 of Fig. 6; i

Fig. 9 is a corresponding section at line 9-9 of Fig. 6;

Fig. 10 is a plan view of the blank after the second rolling step;

Fig. 11 is a longitudinal section along line 11-11 of Fig. 10;

Fig. 12 is a transverse section taken at line 12-12 of Fig. 10;

* atent Fig. 13 is a similar transverse section at line 13-13 of Fig. 10;

Fig. 14 is a cross-sectional view showing the blank of Fig. 10 as related to the forging dies which forge the beads into ribs;

Fig. 15 is a view, corresponding to Fig. 14, of the blank and dies after the closing of the dies;

Fig. 16 is a plan view of the blank after the forging operation;

Fig. 17 is side elevation of the blank illustrated in Fig. 16;

Fig. 18 is a longitudinal central section of the blank;

Fig. 19 is a perspective view of a center section formed by the flash welding of two corresponding half section blanks;

Fig. 20 is a partial cross-sectional view of a beaded blank used in practicing a modified form of the invention;

Fig. 21 is a view, corresponding to Fig. 20, of the bead after bending;

Fig. 22 illustrates the blankof Figs. 20 and 21 after forging of the beads into edge portions;

Fig. 23 is a plan view of an assembled propeller blade, illustrating the relative locations of the center sections made under the invention and other sections of the blade;

Fig. 24 is a partial longitudinal section taken along line 24-24 of Fig. 23; and

Fig. 25 is a transverse sectional view of the completed propeller blade, taken at line 25-25 of Fig. 23.

Briefly, the invention provides a method in which the blank for half of a center section is first heated to forging temperature and then forged to provide beads near two opposite edges thereof. The blank is then longitudinally rolled to the length desired and tapered longitudinally from one end to the other while at the same time the transverse edges are formed so that they are thickened for subsequent joining to other sections of the blade. The tapered blank is next subjected to a forging operation which forms the longitudinal beads to cause the same to extend normally to the plane of the body of the blank and provide longitudinally extending ribs. The half sec tion blank is next heated and placed in a die for a short time to anneal the same and to straighten any irregularities occasioned from the previous step. The formation of the center section is completed by flash welding the ribs of the half section blank to the ribs of a corresponding blank formed in the same way.

In accordance with the invention a blank of high strength and ductility and of suitable size and thickness is cut from alloy steel stock. By way of example, the blank may be approximately eleven by nine inches, and a tongue 1 may be provided along the longest edge for entering the blank into the rolls during subsequent rolling operations.

The blank is then heated to forging temperature,

' placed in a confining die, and forged to form beads 2 parallel with and spaced a short distance from each of the shorter edges of the blank. In order to providestock for rolling, the dies used in this forging step are preferably shaped so that a thickened portion 3 is formed on the opposite side of the blank from each of the beads 2. In addition, the beads 2 are tapered during forging, as illustrated in Fig. 3, so as to be relatively higher at the end of the blank which is opposite tongue 1 previously described.

As an alternative to the first forging step, beads 2 may be initially formed by passing the heated blank between a pair of rolls having grooves corresponding to the beads 2 and thickened portions 3. The rolling also may be performed by using a die and a single roll of suitable configuration.

Because of the use of confining dies during the first forging step, the size of the blank is maintained sub stantially the same. Where rolling is used instead of forging, the size of the blank may be appreciably increased as the beads are initially formed. The blank is next rolled longitudinally of the'beads 2 to increase the size of the blank and to taper it longitudinally so that the portion lying between the heads is relatively thick at the tongue end and. relatively thin at the opposite end. The longitudinal edge portion of the blank, outboard of beads 2, are not tapered, however, since it is desirable that these edges be maintained of uniform thickness for subsequent flash welding toother parts of the propeller blade.

During the first rolling step, if the blank was nine inches in length, the length is increased in rolling to approximately fifteen inches, but the width of the blank is only slightly increased. Due to the fact that the blank is entered into the rolls at the tongue 1 end and is substantially lengthened longitudinally of the heads, the taper in the beads resulting from the first forging step is largely used ,up in rolling stock with the result that the beads are only slightly lower at the tongue end than at the opposite end.

One of'tb'e rolls used in the first rolling operation is grooved to operate on beads 2, but the roll engaging portion 3 is not grooved. The thickened portion 3 obtained in the initial forging step is accordingly used as stock which is rolled into the body of the blank. The blank after rolling has the cross section illustrated in Figs. 8 and 9.

The blank is then subjected to a second rolling step wherein the blank is rolled longitudinally. In this rolling operation the length of the blank is increased and the transverse edges are thickened so that strong flash welds may be made between these edges and adjoining transverse edges of other sections of the blade. The longitudinal edge portions of the blank are preferably left unthickened, except at their ends, to match the thickness of the leading and trailing edge section to which the longitudinal edges of the completed center section are subsequently flash welded.

A blank of substantially the dimensions stated in connection with the first rolling step may be lengthened during the second rolling operation from fifteen inches to approximately twenty-five inches, but again the width of the blank is maintained substantially constant.

As in the case of the first rolling step, the center foil portion between the beads 2 is tapered longitudinally, with the thicker cross section at the tongue end, whereas the longitudinal edge portions outboard of the beads are not tapered. The direction of bead taper, however, is reversed, so that the beads are relatively high at the tongue end and taper in accordance with the taper of the center portion of the blank. This is because it is desired not only that the individual walls of the propeller blade be tapered from shank to tip but that the foils of the blade gradually converge outwardly to the tip after the ribs formed from the beads 2 are welded to the ribs of a corresponding half section as will be described subsequently.

The contour of the rolls used in the second rolling step is such that the beads 2 are tapered in width as well as in height, so that the beads are relatively wide at the torgue end of the blank and narrow at the opposite en The previously referred to thickening of the transverse edges or ends of the blank is efiected during the second rolling step by using rolls having contours which are accurately defined to conform to the shape desired. The thickening occurs along the entire transverse edge portions of the blank, between the beads 2 and laterally outboard of the beads. In addition, the ends of the beads are thickened,.as'shown in Fig. 10, and they may be increased in height, although this is not shown in the drawings.

The thickened portions at the transverse edges of the blank are each shaped with a longitudinal rise which terminates infa level end portion, so that a uniform cross section is maintained during subsequent flash welding to adjoining sections of the blade. Since a considerable amount of metal is burned off during welding, the level end portion is preferably made approximately half an inch in width. 1

Upon completion of the longitudinal rolling step, the ends of the blank are provided with suitable indexing portions 4 and the beads 2 are forged into ribs. To accomplish this, the beaded blank is placed on a fixed bed of a die, as shown in Fig. 14, and movable die members 7 to the right and left of the bed are moved simultaneously toward the fixed bed. At the same time, pressure is exerted downwardly against the top surface of the blank, that is to say the surface opposite the beads 2, by a third movable die member. The simultaneously combined movement of these three members toward the die bed with the half-section blank disposed thereon causes the downwardly extending beads 2 to be formed into rib members, as shownin Fig. 15, which are substantially normal to the body of the blank.

The shape of the dies used in the forging operation is such that the ribs 5 are formed in general accordance with the shape of the heads 2. They are therefore tapered,

both in height and in width, and thickened at their ends for improved fiash welding to adjoining sections of the blade. 7

Because of the rather severe working of the blank due to the rolling and forging operations it may be necessary to stress-relieve the same. It is also desirable to straighten all portions of the blank, particularly the reinforcing ribs, before the ribs are welded to like ribs of a complementary blank.

To accomplish the above desired results the blank is placed in a furnace and heated to approximately 1300" F. As the blank is removed it is immediately placed in a suitable die and permitted to remain there for approximately 30 seconds. During this cooling period the various portions of the blank are held by the die in the desired configuration.

If it is desired to form a center section which has longitudinal strengthening ribs of substantial depth, such as would be the case in connection with the center section immediately adjacent the shank, a modification of the method above described is practiced.

Under the modification, a beaded blank is first formed in the same manner as under the first embodiment, with the width of the portions between the beads 6 and the edges 7 being made quite substantial. The blank as shown in Fig. 20 is then subjected to a press forming operation to form the edges '7 downwardly, as shown in Fig. 21, and provide strengthening ribs. The blank is next subjected to a forging step which shapes the longitudinal beads 6 into edge portions illustrated in Fig. 22. Be cause of this reversal of function between beads and edge portions, the tapers mentioned in connection with the first embodiment of the invention may be inapplicable to the modification.

The blanks formed under the modification are then heated and placed in a die to anneal and straighten as in the case of the first embodiment.

In the last step, under both embodiments of the invention, the indexing portions 4 are removed and two complementary blanks are joined together by flash welding the oppositely disposed ribs of the respective blanks together as shownin Fig. 19. The inner and outer Weld seams are then cleaned by removing any excess metal and the completed section is ready to be joined to other sections of the blade.

Various embodiments of the invention may be employed within the scope of the accompanying claim.

I claim:

A method'of making a center section for a hollow aircraft propeller blade which comprises heating a platelike 'metal blank to forging temperature, forging said blank to form beads on one surface of the blank adjacent two opposite edges thereof, rolling the beaded blank to increase the length thereof, thereafter again rolling the beaded blank to form thickened opposite transverse edges for Welding and to further extend the length thereof, forging the beads to form ribs disposed normally to the plane of the body of the blank, heating the forged blank and placing the same in a die for stress relieving and straightening, and thereafter flash welding the ribs of said blank to similarly formed ribs of a complementary blank to complete the section.

References Cited in the file of this patent UNITED STATES PATENTS 1,937,966 Junkers Dec. 5, 1933 6 McKee Mar. 18, McKee Nov. 18, Murray et a1 June 6, Tiedeman June 24, Gruetjen May 31, Bucher et a1 May 9, Stulen July 11,

FOREIGN PATENTS Great Britain Apr. 1, Italy Nov. 21, 

